1. Field of the Invention
This invention relates to a rear projection type projector and particularly to a rear projection type projector with projection light projected from the rear of a screen projection surface and its method of use.
2. Description of the Related Art
FIGS. 7(a) and (b) are schematic sectional views of a conventional rear projection type projector, particularly, as a rear projection type projector installed in a playing apparatus, wherein the configuration of FIG. 7(a) is for direct projection, and the configuration of FIG. 7(b) is for projection by way of a reflector.
In FIG. 7(a), a rear projection type projector 5 has a projection unit 10 projecting projection light modulated according to image information and a screen projection surface 30 (shown in slants therein), an optic axis R-S (shown in a dotted line in therein) matching a normal direction N-N of the screen projection surface 30. Consequently, an image faithful to image information is reproduced on the screen projection surface 30. (For example, refer to Japanese Unexamined Patent Publication No. 7-155442 (Page 3, FIG. 1))
Also, in FIG. 7(b), a rear projection type projector 6 has a reflector 20, causing the optic axis (shown in a dotted line in therein) to change its direction at a right angle by using the reflector 20. Namely, projection light (optic axis R-M) emitted from the projection unit 10 in parallel to the screen projection surface 30 is reflected by the reflector 20 to become an optic axis M-S matching the normal N-N of the screen projection surface 30 to be projected to the screen projection surface 30. Now, 40 is a screen frame holding the screen projection surface 30, and 50 is an enclosure in which the screen frame 40 is installed and equipment not illustrated is housed. (For example, refer to Japanese Unexamined Patent Publication No. 7-155442 (Page 4, FIG. 12))
However, since conventional rear projection type projectors 5 and 6 are for reproducing a image of image information on the screen projection surface 30, if the image information is given, for example, by a rectangular liquid crystal panel in an aspect ratio of 4:3 or 16:9, an image actually shown on the screen projection surface 30 (hereinafter referred to as an “actual projection range”) becomes rectangular in the same aspect ratio as the aspect ratio of the liquid crystal panel.
FIG. 8 is a front view schematically explaining the actual projection range ratio in the conventional rear projection type projector. A substantially elliptic range EFGH shown in slants therein is a range which a player is able to recognize visually (hereinafter referred to as an “effective projection range”). This effective projection range EFGH may be in various shapes, for example, a rectangle, circle, sector and the like depending on the game machine. On the other hand, a rectangular range TUVW shows an actual projection range of light projected from the projection unit 10.
Now, to facilitate explaining, the screen projection surface 30 is supposed to be set up in a range equal to the effective projection range EFGH, so that light actually projected (actual projection range TUVW) is also supposed to be projected to the screen frame 40 holding the screen projection surface 30. On the other hand, if the screen projection surface 30 is sufficiently wide, the entire actual projection range TUVW is within the screen projection surface 30, part of which is supposed to be recognized visually.
At this time, because the effective projection range EFGH is limited to part of the actual projection range TUVW, a hollow rectangular range (hereinafter referred to as an “invalid projection range”) composed of the actual projection range TUVW from which the effective projection range EFGH is removed is subject to irradiation of light in the same way as the effective projection range EFGH, even though it is not recognized visually by the player. Hence, there was a problem of a reduction in efficiency of light utilization in an actually effective range.
Further, to house an effective projection height E-G in the vertical direction within an actual projection range, it is necessary to enlarge an actual projection width in the horizontal direction to a width shown by A-A in the figure, hence, the actual projection width Q-Q enlarges more than necessary relative to the effective projection width Q-Q (the ratio of actual projection width Q-Q relative to the effective projection width F-H is large). Namely, there was a problem that as an image was expanded excessively, the projection distance stretched and the equipment grew in size.
This invention has been made to solve such problems, and it is an object thereof to provide a rear projection type projector by narrowing the invalid projection range to enhance the utilization efficiency of light and shortening the projection distance to enable the equipment to be made small.